Modulation of platelet responsiveness through selective phosphorylation of plasma membrane proteins: Antagonistic eeffects of cyclic AMP and cyclic GMP

³²P phosphorylation of plasma membranes from human blood platelets, under conditions that closely resemble physiological ones (endogeneous phosphate donors and intact platelets in homologous plasma), result in the incorporation of the label mainly in a membrane glycoprotein of apparently high molecular weight (greater than 400 000). Dibutyryl cyclic AMP, an inhibitor of platelet aggregation, specifically increases the degree of phosphorylation of this glycoprotein. Moreover, it has been found that prostaglandin E₁ one of the most potent inhibitors of platelet aggregation which also increases phosphorylation of the same glycoprotein, is significantly more effective than cyclic AMP.Cyclic GMP does not have any apparent effect on platelet aggregation. However, incubation of platelet-rich plasma with both cyclic GMP and cyclic AMP results in a partial recovery of the platelet responsiveness towards ADP-induced aggregation. Coincidently, the degree of phosphorylation of the high molecular weight glycoprotein under these conditions, although still higher than in controls (no nucleotides added), is significantly decreased as compared with cyclic AMP-treated cells. Furthermore, cyclic GMP inhibits the cyclic AMP-dependent protein kinase activity in isolated platelet plasma membranes.These results suggest a central role for this membrane phosphoglycoprotein in the triggering of platelet aggregation and, furthermore, suggest that modulation of its degree of phosphorylation may be exerted through some cyclic AMP/cyclic GMP relationship, which in the basal state might be critical for platelet responsiveness.     

Requirement of trypsin inhibitor for measurement of 3-hydroxy-3-methylglutaryl coenzyme A reductase in intestinal mucosa of rat

A method was developed for the determination of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in the microsomal fraction of crypt cells and villi of rat intestinal mucosa. Addition of trypsin inhibitor to homogenizing and incubation media at a proper concentration appeared inevitable for measurement of the activity of the villi fraction. The reductase in crypt cells was also slightly enhanced by the addition of the inhibitor. Using this technique, the enzyme activity in villi was found to be as active as the crypt cell fraction. Since other types of protease inhibitors were not necessarily effective, it was suggested that specific enzyme(s) inactivates the mucosal reductase in the course of measurement.     

Migration of Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) in the equine oral cavity

Cogley T. P., Anderson J. R. and Cooley L. J. 1982. Migration of Gasterophilus intestinalis larvae (Diptera: Gasterophilidae) in the equine oral cavity. International Journal for Parasitology12: 473–480. Larvae of G. intestinalis pursued a specific migratory pathway within the equine oral cavity en route to the stomach. The larval migration included the following sequence: burrowing in the tongue mucosa, invasion of the interdental spaces, transitory attachment at the root of the tongue and movement to the stomach. The molt from first to second instar did not occur in the tongue, as commonly believed, but between the interdental spaces. Ninety five percent of the larvae invading the interdental spaces were associated with gingiva of the upper molars. SEM analysis revealed further details of the oral migration: (1) air holes excavated in the epithelium which connect with deeper burrows; (2) an intimate association between air holes and posterior spiracles of larvae; (3) precise impressions of larvae in tissue immediately surrounding the most recently formed burrows; and (4) initial larval entry into the tongue through the use of natural disruptions or healing lesions. Factors influencing the development of the oral migration are discussed.     

Radioreceptor assay for epidermal growth factor.

An established cell line of human lung fibroblasts with a high number of surface receptorsfor mouse epidermal growth factor (mEGF) was used to develop a simple and highly sensitive radioreceptor assay for EGF. ¹²⁵I-Labeled mEGF competed mole for mole with unlabeled mEGF for specific receptors. Optimal range for discriminating EGF concentrations in body fluids and tissue extracts by a competitive binding assay was between 5 and 100 ng/ml. Interassay correlation of variation was 8.47% and the recovery of highly purified mEGF added to serum and urine samples was greater than 95%. Human serum and amniotic fluids contained about 24 and 4 ng/ml, respectively, of mEGF equivalents. Concentrations of mEGF in mouse urine and serum were highly variable and were 2- to 10-fold greater than that previously detected by radioimmune assay. Hypophysectomy nearly abolished submaxillary mEGF content in both male and female mice, but testosterone treatment of hypophysectomized animals restored normal concentrations of mEGF to the glands. mEGF added to culture medium disappeared with time as a function of the number of cellular EGF receptors indicating cellular degradation of the growth factor. The radioreceptor assay for EGF is based on the close biologic relationship between the cell receptor site and the native hormone and should prove to be a useful complementary tool to characterize the physiological role of EGF.     

The effect of positive assortative mating at one locus on a second linked locus

Summary Considerations proceed from a model of positive assortative mating based on genotype at one locus, with an arbitrary number of alleles, assuming no selection, mutation, or migration, hypothetically infinite population size, and discrete non-overlapping generations. From these conditions, inferences are made about the genotypic structure at a linked locus, as well as about the corresponding 2-locus gametic structure.The following main results are presented: in the course of the generations, the genotypic structure at the second locus and the 2-locus gametic structure always tend to a limit responsive to the initial conditions concerning the joint genotypic structure at the two loci and the degree of assortativity and linkage. A complete, analytical representation of the limits is given. In particular, if assortative mating is only partial and at the same time linkage is not complete, a population is not able to maintain a permanent deviation of the gametic structure from linkage equilibrium, and thus the genotypic structure at the second locus tends to Hardy-Weinberg proportions. On the other hand, if initial linkage disequilibrium is combined with partial assortative mating and complete linkage (or with complete assortative mating and unlinked loci) the population maintains this disequilibrium and thus the genotypic structure at the second locus need not tend to Hardy-Weinberg proportions. It turns out that the conditions not only of complete linkage, but also of unlinked loci together with complete assortativity, imply no change in gametic structure from the initial structure.In order to demonstrate the influence of several parameters on the speed of convergence to and the magnitude of the respective limits, several graphs are included.     

Timing and Regulation of Nuclear and Cortical Events in the Cell Cycle of Tetrahymena pyriformis*

SYNOPSIS. Using continuous flow cultures based on the chemostat principle, we varied the cell generation times of the ciliate Tetrahymena pyriformis strain GL, from 4.9 to 22.2 hr and studied various parameters of the cell cycle at 28 C. These included: the duration of the periods required for oral morphogenesis, macronuclear division, cell division, G₁ S, and G₂. The size of individual cells was also measured. Independent of the growth rate, the period of oral morphogenesis occurred during the last 90 min of the cell cycle. In all cases macronuclear and cell divisions took place during the last part of these 90 min, and the final macronuclear separation occurred just before final cell separation. The S-period increased slightly, while the G₁ and G₂ both increased in roughly the same relative proportion to the increasing generation times. Slowly growing cells (generation time 20.5 hr) were shorter but broader and somewhat larger in volume than quickly growing cells (generation time 4.9 hr).     

狗静脉注射高渗溶液后的血流动力学分析

在15只戊巴比妥钠麻醉的开胸狗身上观察高渗溶液对血流动力学的影响,主要结果如下:1.静脉内注射50%葡萄糖溶液(3m1/kg,15s 内注毕),规律地引起心动徐缓、动脉血压降低、左心室(-dp/dt)减小、左心室 dp/dt 和心输出量增加,以及肾和股薄肌的血流阻力降低。25%甘露醇溶液具有类似作用。2.切断两侧颈迷走神经后,注射高渗溶液不再能诱发动脉低血压以及肾和股薄肌血流阻力的反射性降低,提示此类效应的传入通路主要为迷走神经。3.在切断迷走神经后注射高渗溶液,还使左心室 dp/dt 进一步增加,表明高渗溶液增强心肌收缩性。根据以上结果似可认为,静脉注射高渗溶液所致动脉血压降低,实质上反映着心输出量的增加不足以抵销外周阻力的减小。     

溶液流动对等电溶菌酶晶体生长的影响

本文对等温自由生长和强制性溶液生长的等电溶菌酶的晶体形态进行了研究,发现这些形态变化与溶液相的流动密切相关,指出生物晶体生长停止是由于生长晶体周围的溶质贫乏造成的;通过某些手段减薄或消除这一溶质贫乏区,就可以保证晶体的持续生长。本文的研究对改善大尺寸晶体的生长提供了一条途径。     

Effect of excess boron on summer and winter squash

The boron tolerance of two summer squash cultivars (Cucurbita pepo L. Aristocrat Zucchini and Peter Pan Scallop) and one winter squash cultivar (Cucurbita moschata Poir. Butter boy) was determined in large, outdoor sand cultures. Boron treatments were imposed by irrigation with culture solutions that contained 1.0, 3.0, 6.0, 9.0, 12.0, or 15.0 mg B L^-1. Relative fruit yields of Zucchini, Scallop, and Butter boy were reduced 5.2%, 9.8%, and 4.3% with each unit (mg L^-1) increase in soil solution B (B_sw)>2.7, 4.9, and 1.0 mg B L^-1, respectively. Reduced yields of all cultivars were attributed to a reduction in fruit number and not fruit size. Boron concentrations in leaves and fruit were directly correlated to B_sw.